Infectious HIV-1 requires gp160 cleavage by furin at the REKR
511↓ motif (
site1) into the gp120/gp41 complex, whereas the KAKR
503 (
site2) sequence remains uncleaved. We synthesized 41mer and 51mer ...peptides, comprising
site1 and
site2, to study their conformation and
in vitro furin processing. We found that, while the previously reported 19mer and 13mer analogues represent excellent
in vitro furin substrates, the present extended sequences require heparin for optimal processing. Our data support the hypothesis of a direct binding of heparin with
site1 and
site2, allowing selective exposure/accessibility of the REKR sequence, which is only then optimally cleaved by furin.
ESR spectroscopy has been used to study the interaction of para-pentylbenzyl hydroxyalkyl nitroxide with the monolayer of water-soluble protected gold clusters having a core diameter ranging from 1.6 ...to 5.3 nm. The solubilization of the nitroxide probe in the more hydrophobic environment of the monolayer strongly depends on the size of the gold core. In particular, the partition equilibrium constant increases as the nanoparticle diameter decreases. These results have been attributed to the different packing of the chains in the monolayer resulting from the different radius of curvature of the investigated nanoparticles. This represents, to the best of our knowledge, the first report demonstrating that the core size of metallic nanoparticles affects the solvating properties of the protective organic monolayer.
EPR spectroscopy has been used to study the interaction of para-substituted benzyl hydroxyalkyl nitroxides with the monolayer of water-soluble protected gold cluster made by a short alkyl chain and a ...triethylene glycol monomethyl ether unit. The inclusion of nitroxide probes in the more hydrophobic environment of the monolayer gave rise to a reduction of the value of both nitrogen and β-proton hyperfine splittings. The spectra also showed selective line broadening attributed to modulation of the spectroscopic parameters as the result of exchange between free and complexed nitroxide. The rate constants were obtained by analyzing the EPR line shape variations as functions of nanoparticle concentration and temperature. This represents, to the best of our knowledge, the first determination of rate constants for the solubilization of organic substrates in a monolayer-protected cluster.
The entry of the human immunodeficiency virus type 1 (HIV-1) into target cells requires the interaction of viral envelope glycoprotein, gp120, with the human CD4 glycoprotein and a chemokine ...receptor, usually CCR5 or CXCR4. The natural ligand for CXCR4 is the chemokine SDF-1 that inhibits entry and replication of X4 HIV-1 strains. SDF-1 is produced in two forms, SDF-1α (68 residues) and SDF-1β (72 residues); the difference between them lies in the additional four C-terminal amino acids in the SDF-1β sequence. Despite the relevance of the N-terminal site in determining the SDF anti HIV-1 activity, SDF-1β has a stronger activity than SDF-1α. Here we demonstrate that a synthetic peptide mapped on the C-terminus of SDF-1β presents inhibitory activity, whereas an analogue reproducing the C-terminal trait of SDF-1α does not show any activity. The opposite biological effect of the two peptides correlates with the type of interaction they each have with heparin and chondroitin sulfate.
The thiiranium hexachloroantimonates 1a, 3, and 5a − c and the thiirenium hexachloroantimonates 6a − c and 7a with exocyclic S-R substituent (R = Me, Et, i-Pr) react at sulfur with dialkyl disulfides ...R‘ ‘SSR‘ ‘ (R‘ ‘ = Me, Et and R‘ ‘ ≠ R) in CD2Cl2 at 25 °C to give S-R‘ ‘ substituted ions. The reaction rates are affected by the steric hindrance of the substituents at sulfur and at ring carbons. t-2,t-3-Di-tert-butyl-r-1-methylthiiranium hexachloroantimonate (2) does not react, and the t-2-tert-butyl-c-3-phenyl-r-1-methylthiiranium (5a) reacts about 100 times faster than the c-2,t-3-di-tert-butyl-r-1-methylthiiranium ion (1a). The analysis of the kinetic data suggests that the sulfonium sulfur undergoes attack by the disulfide in the ring plane from a direction that is parallel to the C−C ring bond. This is also the direction which ensures the maximum overlap with the LUMO of thiiranium or thiirenium ions (determined at the RHF/3-21G*//RHF/3-21G* level). The combined consideration of the approach modality and of the maximum orbital overlap suggests that the nucleophilic substitution at sulfonium sulfur is not an SN2-like reaction but occurs via an intermediate with episulfurane-like structure. The principle of microscopic reversibility will dictate that this is also the first intermediate in the electrophilic sulfenylation of unsaturated C−C bonds.
Synthetic peptides for AIDS research Di Bello, Carlo; Pasquato, Antonella; Dettin, Monica
Current protein & peptide science,
08/2004, Letnik:
5, Številka:
4
Journal Article
Recenzirano
In spite of the relevance of the results obtained through the clinical application of chemotherapeutic agents (reverse transcriptase and proteinase inhibitors) that are able to prolong the life span ...of affected people, acquired immunodeficiency syndrome (AIDS) remains a serious and lethal disease. AIDS is caused by a type 1 human immunodeficiency virus (HIV-1) and formation of a complex among the gp120, CD4 and CCR5/CXCR4 surface proteins represents a key-step in the infection. The use of synthetic peptides reproducing reduced sequences of these proteins has contributed to increase the knowledge of the mechanism that determines the penetration of the HIV viruses into the target-cells. In addition, short peptides with minimum structural requirements for anti-HIV activity hold greater potential as lead compounds for rational drug design than macromolecular proteins. In this context, our studies concern: the role of gp120 V3 loop in CD4 binding, the importance of the N-terminal sequence of HIV CCR5 coreceptor, the potential inhibitory properties of sequences patterned on CXCR4 natural ligand (SDF-1) and the role of secondary structure in determining gp160 enzymatic processing into gp120.
Theoretical investigations have suggested the presence of intermediate mass black holes (IMBHs, with masses in the 100-10000 M{sub sun} range) in the cores of some globular clusters (GCs). In this ...paper, we present the first application of a new technique to determine the presence or absence of a central IMBH in globular clusters that have reached energy equipartition via two-body relaxation. The method is based on the measurement of the radial profile for the average mass of stars in the system, using the fact that a quenching of mass segregation is expected when an IMBH is present. Here, we measure the radial profile of mass segregation using main-sequence stars for the globular cluster NGC 2298 from resolved source photometry based on Hubble Space Telescope (HST/ACS) data. NGC 2298 is one of the smallest galactic globular clusters, thus not only it is dynamically relaxed but also a single ACS field of view extends to about twice its half-light radius, providing optimal radial coverage. The observations are compared to expectations from direct N-body simulations of the dynamics of star clusters with and without an IMBH. The mass segregation profile for NGC 2298 is quantitatively matched to that inferred from simulations without a central massive object over all the radial range probed by the observations, that is from the center to about two half-mass radii. Profiles from simulations containing an IMBH more massive than {approx}300-500 M{sub sun} (depending on the assumed total mass of NGC 2298) are instead inconsistent with the data at about 3{sigma} confidence, irrespective of the initial mass function and binary fraction chosen for these runs. Our finding is consistent with the currently favored formation scenarios for IMBHs in GCs, which are not likely to apply to NGC 2298 due to its modest total mass. While providing a null result in the quest of detecting a central black hole in globular clusters, the data-model comparison carried out here demonstrates the feasibility of the method which can also be applied to other globular clusters with resolved photometry in their cores.
Proteolytic activation of the HIV-1 envelope glycoprotein gp160 is selectively performed by the proprotein convertase furin at the C-terminus of the sequence R508-E-K-R511 (site 1), in spite of the ...presence of another consensus sequence, Lys500-Ala-Lys-Arg503 (site 2). On the basis of the solution structural analysis of the synthetic peptide p498, spanning the gp160 sequence Pro498-Gly516, we previously suggested a possible role of an N-terminal helix in regulating the exposure and accessibility of the gp160 physiological cleavage site, enclosed in a loop. Here we report on the activity and conformation of the 23-residue peptide h-REKR, designed to exhibit a large N-terminal helix, followed by the gp160 native sequence, Arg508-Gly516. h-REKR is digested by furin with high efficiency, comparable to the full native p498. Circular dichroism analyses, in mixtures from pure water to 98 % trifluoroethanol, outline a significant content of helical structure in the peptide conformation. The molecular model obtained from NMR data collected in trifluoroethanol/water, by means of DYANA and AMBER simulations, indeed has helical structure on a large N-terminal segment. Such a long helix does not seem to affect the loop conformation of the C-terminal site 1-containing sequence, which exhibits the same proton chemical shifts already observed for the full native p498.
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